1. Field of the Invention
The present invention relates generally to flow control devices. More particularly, the invention relates to a control valve having multiple seals in a single valve trim. In a particular embodiment, the invention relates to a choke valve having multiple balanced sealing sleeves contained within a single valve trim.
2. Background of the Related Art
Flow control devices are useful for modifying the flow rate in flow channels, conduits or systems. For example, flow control choke valves are useful in fluid pipelines, such as high pressure oil and gas production pipelines where high pressure differentials may exist between the fluid pressure in the upstream and downstream pipelines, between which the valve is disposed. For example, the upstream fluid pressure in a high pressure oil and gas production pipeline may be on the order of 5000 pounds per square inch and the downstream fluid pressure ranging from 0 to 5000 pounds per square inch. Thus, flow control devices may be designed to be capable of operating in high pressure environments.
Flow control devices typically include a reciprocating valve stem threadably or otherwise connected to a valve body. The valve stem carries or is connected to a closure member or a sealing assembly. As it reciprocates, the typical valve stem is capable of engaging and disengaging the closure member with a valve seat (or around an orifice). Fluid pressure within the flow control device may, however, exert undesirable pressure forces on the internal components of the flow control device that are in contact with the flowing fluid, mixture or other media (the valve "trim") and which are associated or connected with the valve stem. This can make reciprocation or movement of the valve stem and thus operation of the flow control device difficult or impossible.
Balanced flow control devices have been contemplated to balance pressure forces on internal components of the flow control device in an effort to reduce or eliminate the resultant pressure forces on the valve stem. To achieve balanced valve trim, balance conduits extending at least partially through one or more internal valve components may be provided. For example, one or more balance conduits may be disposed in the closure member of a fluid control valve. In such example, fluid and thus fluid pressure from the downstream bore can be communicated through the balance conduit(s) to opposing sides or surfaces of the closure member, enabling the closure member to be balanced.
Existing balanced flow control devices include a single balanced closure member or sealing assembly with a single seal in each valve trim. However, for a variety of reasons, it is believed that it would be beneficial to provide one or more additional seals within the same valve trim as that of the single seal. For example, this may be used to provide resilient secondary sealing in the event that the primary non-resilient seal member should fail. Existing balanced control valves are not believed to provide multiple seals or seal members within a single valve trim. In addition, existing balanced control valves do not provide for multiple balanced sealing assemblies.
Accordingly, theres is a need for a flow control valve with multiple sealing assemblies, or seals, within a single valve trim. Ideally, at least in some instances, each of the seals, or multiple sealing assemblies, of such a flow control valve could be balanced. Further, especially well received would be a valve having such feature(s) and which is useful as a choke valve.